This study investigated the accuracy order of English relative clauses in the usage of 199 Japanese high school students of English as a foreign language (EFL). Specifically, it looked at: (1) whether the Accessibility Hierarchy conform to the accuracy order by Japanese senior high school students of EFL; and (2) how frequently this population uses relative clauses. Subjects were given three kinds of tests, in grammaticality judgment, sentence-combining, and translation. Results indicate that this population followed an order matching the Accessibility Hierarchy, and the Perceptual Difficulty Hypothesis to some extent, and that the subjects preferred using relative clauses to present participles and post-modification positions. A pedagogical implication is that center-embedding of a relative clause functioning as object of preposition should be an area of classroom instructional focus. (Author/MSE)